Many complaints blamed the Windows Phone 8 mobile operating system for the reboots, although some users said Microsoft Support personnel had suggested the problem could be related to running a Skype preview app or to running Internet Explorer on the phones.

However, Microsoft Support suggested to one user in the forum named Sweendog_99 to uninstall the Skype preview app, then clear the Internet Explorer history and reset the phone.

Sweendog_99 responded on the forum that taking the steps might have worked since he didn't have any reboots afterward -- that he noticed. However, for many of the users, the reboots happen while the phones are idle and no apps are being actively used.

HTC and Nokia could not be reached for comment, although Nokia told users to reset their phones by turning them off, removing the SIM card and waiting 10 minutes before re-inserting the SIM and then turning on the phone again.

The problems seem to be related to both the Lumia 920 and the HTC 8X phones running on a variety of carriers in both the U.S. and Europe and on both phones regardless of the whether the apps were factory-installed or installed by the user.

Some of the complaints go back to early November, but continued Monday. "Be thankful you're only getting reboots," Martinmc78 told other users on the Windows Phone Central Forum on Monday. He said that since Friday he has been having major problems, including reboots on his HTC 8X on O2 in the UK, SIM errors, messaging not working and more.

Some complaints have also noted battery problems, and possibly phone connection problems to the cellular network. JGraves4480 said early Monday that he went out of town and lost all of his data outside of his home town on a Verizon Wireless HTC 8X. "I'm just wondering if the phones are losing connection with the cell system, causing issues," JGraves 4480 said.

A user named Nicooke on Windows Phone Central said HTC agreed to swap out his 8X because of the reboot problems, but said it would take more than a week to do so. "Just wish they would come out and say what the issue is," Nicooke said.